Fuel prices at German petrol stations are extremely volatile and change several times a day. Over 20 price changes within 24 hours are not uncommon. This can result in price differences of 20 cents per litre. As a general rule, fuel prices are relatively high in the morning (6.30 am to 8.30 am), whereas it is cheaper to fill up in the early evening (5.30 pm to 9.30 pm). If possible, never fill up at motorways! The price at motorway filling stations is often 30% higher than at other filling stations.
In Germany there is an official reporting office to which petrol stations must report their current fuel prices - in real time. You can check the current petrol prices at almost 15000 petrol stations in Germany here. You have to enter a 5-digit postcode:
How much does petrol and diesel cost at petrol stations in Germany? Check fuel prices from ~15000 petrol stations here. In real time!
Information about the official registration office (possibly only in German)